Has my router been hacked or was the Plusnet outage responsible ?

[#1]

From about 4.00 p.m. yesterday, I could no longer access the internet.  Finally, about 11.00 p.m. I telephoned Plusnet to discover that there had been a major outage and all the Plusnet servers were apparantly down.  However, I was assured that this should not have affected my access to the internet, as my DSL light was glowing steady.
So I checked my router and discovered that all the settings had been returned to default, including the gateway user id and password.  I re-set everything and was then able to access the internet.  So far, so good.
However, I am really rather uneasy about this.  What could have zapped the router settings ?  The firewall on the router is set as is the Plusnet firewall and of course the Windows firewall.  Three possibilities occur to me :
1.  The router is very old indeed, a Linksys WAG354G - must be one of the very early models.  It works well apparantly still, but could it be starting to fail ?
2. Some external surge from the WAN / local exchange knocked it out  ?
3. I was hacked ?  My normal security settings are all good.
4. I still use Windows XP and with the ending of MS support, am I already vulnerable to attack ?
5. Somehow this did have something to do with the Plusnet outage ?  This latter just seems to me to be the most likely, as it is almost too coincidental that it happened at the same time.  But Plusnet have assured me that it is not.
No damage done, but if my router is suspect, maybe I should buy a new one.
Any reactions would be appreciated.
Thanks.

[#2]

Hmm that's a bit strange - there's nothing on the Service Information page about a Plusnet outage.
Can you post your router stats?
It's a bit strange your router lost all its settings. Did you hold down any buttons or anything when the internet was down?

[#3]

My money would be on a failing router.
The settings are normally stored in something called NVRAM which hold all your password and connection stuff. Over time these can and do fail - it's rare but happens. Older routers may also use a backup battery which has a finite lifespan.
Routers being knocked out by lightning are quite common but being knocked out by something from the exchange is almost unheard of. Any spike big enough to damage the router would probably have damaged your phone as well.
Hacking is unlikely, especially if you have changed the default password to get into the router.
Did you turn off the power to your router when you had issues connecting ?

[#4]

I agree with DomS on this one.
I've seen it quite a few times where the router details have been completely removed following an outage, a router setup usually fixes things.

Quote

NVRAM which hold all your password and connection

Could quite easily have been this. I would doubt very much that the router has, in any way been compromised.

[#5]

Thanks.  The answer to the two questions are :
1. Andy H..  The Plusnet outage was from yesterday afternoon and I was told by Plusnet that they had no systems and could not even register a ticket for me.  Their system was due to go back live again at 6.00 a.m. this morning, which I suppose it must have done.  My router is under the desk and I have to crawl to reach it - so the answer is "No", I did not hold any buttons down.  All I did after the outage was to remove the power from the router by turning the wall socket off.
2. DomS.  I just turned the power off at the wall socket.  I had changed the user id and password, and was not using the default settings which are the usual just "admin" - that is how I got back in of course, when I realised that my own user id and password was not being accepted any more.  If it happens again, I will suspect the battery but I do turn it off when I go away always, and this has not happened before.
3. Chris Pettitt.  It seems to make sense that maybe the outage did indeed empty the NVRAM somehow.  I re-set everything and everything is working fine now.
So thanks to everyone for their comments.  Very helpful but I think I can relax about hacking from what has been said.

[#6]

It sounds like the outage was a Plusnet issue at their end and shouldn't have affected your connection i.e. the machines they use to view customer information were not working, not an issue with your internet connection.
It could have been an issue solely isolated to your router with no problems with Plusnet at all.